Every search engine has its own algorithm that determines the Ranking of documents within Search Results. A search engine algorithm is a complex set of computer-based rules for how to interpret and rank web pages when users do a search for a particular word or phrase. Its evident that search engines do not publicly disclose the details of such algorithms.
There are lots of similarities in the way search engine algorithms work. To learn more about how search engines work or how to improve your rankings, visit Search Engine Watch to find information on search engines and their rules.